The field of the invention relates generally to fluidic actuators, and more specifically, to fluidic actuators that contain an internal source of pressurizing fluid.
At least some known types of fluidic actuators use pressurized fluids to produce mechanical motion. For example, known piston-cylinder drives include a piston that moves within the chamber of a cylinder. More specifically, a differential in fluid pressure across the piston causes mechanical displacement of the piston, such as occurs in air cylinder drives and hydraulic rams, for example. Although such actuators may have a relatively long stroke, such actuators may be limited in the force applied to the fluid pressure across the piston by the surface area of the piston.
To produce mechanical motion, at least some other known fluidic actuators simulate the action of natural muscle contraction. For example, in some known actuators, an elastic tube or bladder is surrounded by a sleeve or sheath of relatively stiff, yet flexible material such that an inner bladder is defined between the sleeve and the tube. The two ends of the sheath/tube apparatus can then be connected by end fixtures to other mechanical structures. For example, the sheath/tube apparatus may be connected within an aircraft control system behind the rearmost wing spar to facilitate moving the aircraft control surfaces between extended and retracted positions for varying the lift or drag of the wing. When a pressurized fluid, such as air or hydraulic fluid, is supplied into the inner bladder, a pulling force may be induced axially in the tube as a result of the expansion of the tube. The pulling force forces the surrounding sheath outward and draws the two ends of the actuator closer together. Moreover, a resultant tensile force is then applied to structures attached to the actuator. However, the internal space created by the expansion of the actuator as a result of the pressurization requires an additional volume of compressed gas to be supplied in order to continue to actuate the device.